Attaching track to foamboard?

[RobertInOntario]

As some of you may know, I've been working on a small HO layout that is made from green insulation foam board.

So far, I've been attaching the track to the foam using the typical pins or spikes. Of course, these don't attach that well into the foam so the spikes are only temporarily holding the track down.

What's the best type of glue to use for attaching track to the foam -- is white glue good enough or is there something better?

I guess I could just start ballasting and then the glue and ballast would hold the track down.

Thanks,
Rob